A nonaqueous electrolyte battery is charged and discharged by the movement of lithium ions between the negative electrode and the positive electrode. Carbonaceous materials are used for the negative electrode active material of the nonaqueous electrolyte battery. Nonaqueous electrolyte batteries using negative electrode active materials having a higher Li inserting and releasing potential than carbonaceous materials have recently been studied and developed. Among these negative electrode active materials, spinel type lithium titanate is a promising negative electrode active material having excellent cycle characteristics and high safety because it is free from a volumetric variation attendant upon a charge-discharge reaction.
A nonaqueous electrolyte battery using a negative electrode active material, for example, spinel type lithium titanate, which has a higher Li inserting and releasing potential than carbonaceous material, has less possibility of the occurrence of lithium dendrite as compared with the case of using a carbonaceous material and therefore has high safety. Also, this spinel type lithium titanate is ceramics and is therefore resistant to thermorunaway.
A nonaqueous electrolyte battery using spinel type lithium titanate (for example, Li4Ti5O12) as the negative electrode has the problem of a low energy density and therefore, a negative electrode active material having a high capacity is required. In light of this, studies are being made on titanium oxide compounds such as TiO2 (330 mAh/g) having a theoretical capacity per weight higher than that (170 mAh/g) of Li4Ti5O12 (for example, T. Ohzuku, T. Kodama, T. Hirai, J. Power Sources 1985, 14, 153, R. Marchand, L. Brohan, M. Tournoux, Material Research Bulletin 15, 1129 (1980)).
TiO2 has many crystal structures such as an anatase type and rutile type. Anatase type TiO2 is well known as the battery active material. However, it is considered difficult to develop a high-capacity battery using anatase type TiO2 although anatase type TiO2 has a reversible capacity of about 160 mAh/g which is a high theoretical capacity.
Recently, there has been a report that titanium dioxide having a monoclinic structure which is one of the crystal structures of TiO2 is a promising battery material as a high-capacity negative electrode material (for example, JP-A 2008-117625 (KOKAI)). Titanium dioxide having the monoclinic structure can provide a reversible capacity of about 240 mAh/g and is therefore expected to develop a high capacity.
However, it is necessary that titanium dioxide having the monoclinic structure be micronized to obtain a high reversible capacity. This is accompanied by an increase in specific surface area, leading to a problem concerning a reduction in first cycle Coulomb efficiency.
JP-A 2007-18883 (KOKAI) proposes a method in which lithium-titanium composite oxide particles having an average pore diameter of 50 to 500 Å are used with the intension of improving the large-current characteristics and charge-discharge cycle characteristics of a nonaqueous electrolyte battery. Also, JP-A 2007-18883 (KOKAI) discloses that the energy density of a battery is improved when the volume of pores having a diameter of 10 Å or less in the lithium-titanium composite oxide particles is limited to 0.001 mL/g or more.